This is to write a BGL graph object into an output stream in the
GraphML format. Both overloads of write_graphml will emit all of
the properties stored in the dynamic_properties object, thereby
retaining the properties that have been read in through the dual
function read_graphml. The second overload must be used when the
graph doesn't have an internal vertex index map, which must then be
supplied with the appropriate parameter.

A directed or undirected graph. The
graph's type must be a model of VertexListGraph. If the graph
doesn't have an internal vertex_index property map, one
must be supplied with the vertex_index parameter.

IN: VertexIndexMapvertex_index

A vertex property map containing the indexes in the range
[0,num_vertices(g)].

IN: dynamic_properties&dp

Contains all of the vertex, edge, and graph properties that should be
emitted by the GraphML writer.

IN: boolordered_vertices

This tells whether or not the order of the vertices from vertices(g)
matches the order of the indexes. If true, the parse.nodeids
graph attribute will be set to canonical. Otherwise it will be
set to free.